The response to chloroquine of a strain of Plasmodium falciparum malaria from Colombia, South America, has been studied in seven patients. Six of these infections responded poorly to normal (0.6 gram, 1.5 grams) and above normal (2.1 grams) doses of the drug. The parasites were either not cleared from the blood stream or were eliminated slowly, after which they relapsed quickly. In two instances, 1.5 grams of chloroquine failed to eliminate the parasitemia; and, in two other instances, the parasites increased after a 600-mg single dose.
These findings indicate that this strain of malaria is resistant to the usual doses of chloroquine. The resistant quality was still present after mosquito passage.
Because of the widespread use of this drug for the suppression and cure of malaria and especially in malaria eradication programs, the occurrence of resistance by the parasites appears to be of considerable importance.
Department of Health, Education, and Welfare, Public Health Service, National Institute of Allergy and Infectious Diseases, Laboratory of Parasite Chemotherapy, National Institutes of Health, Bethesda, Maryland.
University of Texas Southwestern Medical School, Department of Microbiology, Dallas, Texas.